A number of systems and programs are offered on the market for the design of parts or assemblies of parts, such as the one provided by the applicant under the trademark CATIA. These so-called computer-aided design (CAD) systems allow a user to construct and manipulate complex three-dimensional (3D) models of parts or assembly of parts. A number of different modelling techniques can be used to create a model of an assembly. These techniques include solid modelling, wire-frame modelling, and surface modelling. Solid modelling techniques provide for topological 3D models, where the 3D model is a collection of interconnected edges and faces, for example. Geometrically, a 3D solid model is a collection of trimmed or relimited surfaces that defines a closed skin. The trimmed surfaces correspond to the topological faces bounded by the edges. The closed skin defines a bounded region of 3D space filled with the part's material. Wire-frame modelling techniques, on the other hand, can be used to represent a model as a collection of simple 3D lines, whereas surface modelling can be used to represent a model as a collection of exterior surfaces. CAD systems may combine these, and other, modelling techniques, such as parametric modelling techniques. CAD systems thus provide a representation of modelled objects using edges or lines, in certain cases with faces. The modelled objects comprise a number of lines or edges or other elements. These elements may be acted upon by the user of the system in the design process. The user may wish to select or designate one given element in the modelled object, for instance for displaying its properties, erasing or cancelling it, or for being able to act upon the selected element. The prior art suggests using a haptic device such as a mouse for selecting elements in a design system, as explained below. The prior art solutions are explained in reference to a mouse; displacements of the mouse result in displacements of a cursor on the computer display. The mouse is provided with a button, which the user may act upon for “clicking”.
A known solution for selecting an element displayed on the display of a computer system is to select the element over which the cursor of the mouse is placed at the time the user clicks on the mouse button. In such a system, the user needs to move the mouse, so that the cursor on the display is above the element to be selected. When this is the case, the user presses the button of the mouse for selecting the element. This solution requires the user to move the mouse, so that the cursor is above the element to be selected; this may result in numerous movements of the mouse when various objects have to be selected. This may also cause problems where elements to be selected are close one to the other on the display; indeed, the user may select an element which is not the relevant one, but which happens to be close to the relevant one.
To address the problem of selection of an element, it was proposed to highlight the element over which the cursor is located. This solution is used in the CAD system provided by Dassault Systemes under the trademark CATIA; in this system, an element is highlighted on the display when the cursor of the mouse lies within the boundaries of the element on the display. This results in the user being provided, at any time, with an indication of the element he would select if he clicked on the mouse button. This solution addresses the problem of selecting an element among several elements on the display.
The prior art also suggests using picking zones for helping a user in selecting an element on the display. A picking zone is a virtual zone of the display, which is associated to a displayed element and extends beyond this element. Whenever the cursor is within the picking zone, a click on the mouse button results in the associated element being selected. This solution is used in the menus of Microsoft® Word 2000: each icon or text representative of a function in the menu or in a tool bar is provided with a rectangular picking zone. When the user moves the mouse so that the cursor travels over the various items of a tool bar, the corresponding picking zone is highlighted. Providing such a picking zone makes selection easier, since the mouse cursor does not have to be exactly over the relevant element for permitting this element to be selected. However, such picking zones are easy to define in a menu or in a tool bar, where the position of the different objects is predetermined, so that the picking zones may also be predetermined.
Another issue in design systems is to allow the user to act on displayed elements—for instance for changing the shape of a displayed element. One prior art solution is to provide displayed elements with handles, which may be selected by the user. Such handles are exemplified in FIG. 1, in the case of an image created in Microsoft® Word 2000. FIG. 1 shows an ellipsis 2, which has nine handles. Handles 4, 6, 8 and 10 are located at the respective corners of a rectangle containing the ellipsis and the sides of which are respectively parallel to the major and minor axes of the ellipsis. Handles 4, 6, 8 and 10 may be used for sizing up and down the ellipsis, in a proportional transformation centred on the opposed handle; this is done by placing the cursor over one of the handles, pressing the button, dragging the handle to the appropriate location and releasing the handle. Handles 12, 14, 16 and 18 are located at the middles of the sides of the rectangle and are used for lengthening or shortening the ellipsis, in directions parallel to the sides of the rectangle. Last handle 20 is used for rotating the ellipsis, around a centre of rotation located substantially in the middle of the ellipsis. The handles in this prior art system only appear when the element is selected. For instance, in FIG. 1, the handles only appear when the ellipsis is selected, that is when the user clicks on a point which lies within the ellipsis. Each handle has a picking zone, which helps the user in selecting and dragging the handle.
Handles, like picking zones, still require the user to move the mouse, so that the cursor travels over the display. In a design system, or more generally in any system where there are numerous elements to select or handles to act upon, this results in the mouse being displaced over considerable distances. In addition, for selecting elements, there is a need to place the mouse cursor exactly over the element or over the picking zone of the element. This requires the user to pay attention to the specific location of the mouse.
Thus, there exists a need for a solution, allowing a user of a computer system to select elements displayed on the system. The solution should preferably be easy to understand and use, and should preferably avoid important movements of the mouse or haptic device. Preferably, it should also avoid the need for the user to place the mouse at very specific locations.